The present invention relates to improvements in an automatic document feeder used for a recording device or an image reading device of an electrophotographic copier, and more particularly relates to improvements in a circulation type automatic document feeder having a document feeding mode (RDH) in which one-sided or two-sided documents stacked on a document stack section are separated from the document stack one by one and fed to an image reading section and then the document is returned to the document stack section so that it can be repeatedly fed, and also having a two-sided document reversal feeding mode (R-RDH).
An automatic document feeder (ADF) that can efficiently and automatically feed a document on which an image is recorded, has already been provided to a recording device of an electrophotographic copier or a recorded image reading apparatus.
An automatic document feeder (RADF) having a reversal function by which a document is reversed, is put into practical use as a copier by which the images on a two-sided document are copied onto one side or both sides of a recording paper and as an image reading apparatus by which the images are read.
Also, a circulation type automatic document feeder (RDH) has been proposed in which the documents stacked on a document stack section are separated one by one and automatically fed onto a platen glass and the document exposed on the platen glass is returned to the document stack section so that the document can be repeatedly processed.
By this circulation type automatic document feeder (RDH), a copy is made when a document is circulated once, so that the document is circulated by the number of required copies.
Moreover, a circulation type automatic document feeder (R-RDH) has been also provided in which a document reversal mechanism is added to the RDH described above (disclosed in Japanese Patent Application Open to Public Inspection No. 197246/1989).
By these circulation type automatic document feeder (RDH and R-RDH), which will be referred to as RDH hereinafter, it is possible to conduct a high speed continuous copying operation and to quickly collate copied recording papers. Moreover, when the circulation type automatic document feeder (RDH) is combined with a finisher device by which stapling and punching operations are conducted on the recording papers, the overall recording operation can be automatically performed.
The aforementioned RDH device is of a bottom-feed-top-return type in which: a plurality of documents are stacked on the document stack section under the condition that the front surfaces of the documents are set upward; and the lowermost document is separated from the document stack one by one and conveyed to the processing section (the platen glass surface).
In the bottom-feed-top-return type apparatus described above, when a document is sent out from the document stack, the front surface of a document and the back surface of another document are rubbed with each other, so that the image on the rubbed document is damaged and further the front and back surfaces of a document are stained. Especially when a document is written with a pencil, the document is remarkably stained.
In order to solve the above problems, a top-feed-bottom-restack type RDH apparatus has been disclosed in Japanese Patent Publication No. 37536/1981. In this apparatus, a processed sheet is inserted under the sheet stack with a cyclic operation type stack lifting means.
The following problems may be encountered in the top-feed-bottom-restack type RDH.
In a sheet accommodation and supply device disclosed in Japanese Patent Application Open to Public Inspection No. 205273/1991, returned documents are reversed and inserted from the bottom portion of a document stack on the downstream side of document feeding in an RDH device, and a vertical presser member is disposed at the rear end position of an upper document stack. Technique disclosed in Japanese Patent Application Open to Public Inspection Nos. 116671/1992 and 116672/1992 is concerned to a reversal document conveyance direction, in which a direction changeover claw to change over between the normal and reverse conveyance is provided so that the conveyance passage can be changed over.
The following problems may be encountered in the top-feed-bottom-restack type RDH.
(1) Structure of the cyclic operation type lifting means is complicated. PA1 (2) In the case where an end portion of a sheet to be inserted under the stack is curled, there is a high possibility that the end portion is caught by the cyclic operation type stack lifting means. PA1 (3) When a sheet is returned at high speed, the operation of a document feeder becomes complicated, so that the operation becomes unstable. PA1 (4) Each time a sheet is returned, the stack lifting means is moved upward and downward, so that noises are caused. PA1 (5) It is difficult to adjust the apparatus when the sheet size is changed. PA1 (1) Noises are made by the suction fan means, and its manufacturing cost is high. PA1 (2) In the structure in which a plurality of thin belts are disposed, a document conveyed on the belts is not uniformly contacted with the belts because there are gaps between the belts, so that the document surface is formed into a wave-shape, and the protruded portions at the leading end of the document on the belts collide with the trailing end of an upper document. As a result, documents are jammed.
In order to overcome the above disadvantages, the invention disclosed in Japanese Patent Application Open to Public Inspection No. 217568/1992 is constructed in the following manner: The circulation type top-feed-bottom-return automatic document feeder includes an upper suction fan means, an upper feeding belt type document feeding means, and a lower document return rotation means composed of a plurality of thin belts.
However, in the automatic document feeder constituted in the aforementioned manner, the following problems may be encountered, so that improvements are required.
In order to overcome the aforementioned disadvantages, the present invention is to provide a circulation type automatic document feeder of an upper-feed-bottom-insertion system stably operated even when documents are fed at high speed and further the document feeder can handle various sizes of documents.
The first object of the present invention is to provide an automatic document feeder, the copying time of which can be reduced when a conveyance interval between a previous and a successive document is shortened to a minimum distance by a simple structure and control, and the copying time can be also reduced when the conveyance time for conveying a plurality of documents to an image reading unit is remarkably reduced by carrying out preparatory paper feeding.
In the circulation type automatic document feeder, documents subjected to image reading processing are circulated onto the document stack unit so that they can be fed again. Therefore, it is necessary to accurately align and stack the documents that have been discharged from the paper discharging means. Also, in the case of the ADF and R-ADF modes, when discharged documents are not aligned on the document stack unit, they are scattered or dispersed out of the tray, which causes problems in the copying operation.
In order to prevent the discharged documents from being scattered or dispersed in the conventional automatic document feeder, the related technique is disclosed in Japanese Patent Publication Open to Public Inspection Nos. 140280/1992, 164786/1992 and 164787/1992, and also disclosed in Japanese Patent Publication Open to Public Inspection No. 217568/1992 and Japanese Patent Application No. 209199/1992 applied by the present inventors.
In the case where the document discharging speed is relatively low, the momentum of the document is small. Therefore, the documents can be properly aligned when they are discharged onto the document stack unit. However, when the document discharging speed is increased, the leading end of a document is not accurately contacted with a stopper provided on the document stack unit when the document is discharged, so that the document overruns. As a result, the document is deformed or bounded, and further the document can not set at a predetermined position. In the case of the ADF mode or R-ADF mode, the discharged documents are scattered out of the discharging tray.
In the case of a high speed type copier in which a plurality of documents are successively fed onto the image reading unit (platen glass) at short intervals so as to improve the copying productivity, the document replacing time is increased when the previous document conveyed by a conveyance means is discharged at a low speed, because the conveyance of the following document conveyed at the same speed is delayed. In the case where only the discharging speed of the previous document is lowered, the successive document closely approaches the previous document, so that the trailing end of the previous document collides with the leading end of the successive document, thereby resulting in defective conveyance. In the case where a document feeder includes a conveyance means that conveys a returned document in synchronization with the leading end of a document, it is difficult to synchronize the leading end with the document.
In the copiers disclosed Japanese Patent Publication Open to Public Inspection No. 217568/1992 and Japanese Patent Application No. 209199/1992, which have been described before, an upper guide for documents returning to the document stack unit is not provided, so that the returned documents are greatly curled, and further they can not be properly aligned. In this case, documents are conveyed, using their own weight. Accordingly, when the number of documents is small, a sufficient conveyance force can not be provided.
The second object of the present invention is to provide a circulation type automatic document feeder in which a top-feed-bottom-return operation is carried out so that a document returning to the document stack unit can be positively returned to a document feed start position.